Apparatus and method for resource allocation

ABSTRACT

The present invention relates to a method and an arrangement for resource allocation in a packet transmission network including at least one link ( 19 ). According to the invention the following steps are performed: Determining link resource status. If link congestion is determined then: determining if it is possible to allocate more link capacity, allocating more link capacity when it is possible to allocate more link capacity, and alleviating link congestion using Active Queue Management when it is not possible to allocate more link capacity.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to the handling of link and cellcongestion in packet transmission networks and more particularly to theearly detection of congestion and the implementation of mechanisms forobviating the consequences of congestion.

DESCRIPTION OF RELATED ART

In packet based communication systems, i.e. in which information to betransmitted is divided into a plurality of packets and the individualpackets are sent over a communication network, variable bit rates occur.It is therefore known to provide queue buffers at various points in thenetwork to accommodate for sudden bursts in the load.

A phenomenon that is known in packet transmission networks is that oflink congestion. Link congestion implies a state in which it is notpossible to readily handle the number of data packets that are requiredto be transported over that connection or link. As a consequence ofcongestion at a given link, the number of data packets in a queue bufferassociated with said link will increase and buffer over-load will occur.In response to a link congestion condition, it is known to implement adata packet dropping mechanism referred to as “drop-on-full”. Accordingto this mechanism, upon receipt of a new data packet at the queuebuffer, a queue length related parameter, such as the actual queuelength or the average queue length, is compared to a predeterminedthreshold. If the predetermined threshold is exceeded, then a datapacket is dropped. The threshold indicates the “full” state of thequeue.

The so-called “Transmission Control Protocol” (TCP) is a commonly usedprotocol for controlling the transmission of packets over an IP network.When a TCP connection between peer hosts is initiated, TCP startstransmitting data packets at a relatively low rate, i.e. so called “slowstart mode”. The transmission rate is successively increased in responseto receipt of acknowledgement from the receiver. If data packets aredetected as missing, then TCP interprets this as an indication ofcongestion and reduces its load.

Compared to wired networks, wireless links are equipped with a ratherlimited capacity. This is why it can be expected that the wireless linkwill often be the bottleneck of an end-to-end connection. This meansthat excessive load of a TCP connection will eventually build up in thebuffer prior to the congested link. Since the buffer contributes to theend-to-end delay, it is desirable to keep the buffer as small aspossible since large delays cause sluggishness to interactive traffic.At the same time, however, the buffer should be large enough to smoothout load variations, in order to utilise the capacity allocated for thelink.

Further, the dynamics of TCP is strongly dependent how or in which ordersegments are discarded. Consecutive segment losses are likely to put theconnection into TCP slow start, which is particularly bad forhigh-latency links, such as wireless links.

To fulfil these requirements on the buffer, Active Queue Management(AQM) may be used. The principle of Active Queue Management is to detectcongestion at an early stage, before the buffer overflows. Whencongestion or near congestion is detected, it is alleviated by e.g.discarding packets or signalling congestion using Explicit CongestionNotification (ECN) according to some given Active Queue Managementalgorithm. Typically, an algorithm is used for indicating congestion,without discarding all incoming packets.

Random Early Detection (RED)—see e.g. Floyd, S. and Jacobson, V. “RandomEarly Detection Gateways for Congestion Avoidance”, IEEE/ACMTransactions on Networking, 1(4), August 1993—is an Active QueueManagement method that has found wide acceptance within InternetRouting. The RED principle is that an incoming packet is accepted if thequeue level is less than a low fixed queue threshold, but discarded ifthe queue level is greater than a high fixed queue threshold. Forintermediate queue fill levels, incoming packets are discarded with acertain probability.

Other solutions for Active Queue Management algorithms are alsodescribed in EP 01107850.8 (filed, but not published at the filing dateof the present application) and GB 0113214.1 (filed, but not publishedat the filing date of the present application).

In systems with limited resources, congestion may also occur in a largerconcept than in the individual link and some sort of resource managementmay therefore be employed. This is especially the case in mobilenetworks.

A mobile network includes among other things a set of base stations ornode Bs, each serving a given cell or a number of cells. A mobilestation or user equipment may connect to one or more base stations tomake or receive a call. If the mobile station moves from one cell toanother during a call, handover may occur, meaning that the mobilestation now communicates with another cell and possibly another basestation. Different types of handover exist.

A link is in this context a service provided for transmission of datapackets between a mobile network and a mobile station or user equipment.Communication from the mobile network to the mobile station or userequipment is referred to as a downlink, while communication from themobile station or user equipment to the mobile network is referred to asan uplink.

The code division multiple access (CDMA) communication method wasdeveloped to allow multiple users to share radio communicationresources. In the general CDMA method, each user is assigned a uniquecode sequence to be used to encode its information signal. A receiver,knowing the code sequences of the user, can decode the received signalto reproduce the original information signal. The use of the unique codesequence during modulation provides for an enlarging of the spectrum ofthe transmitted signal resulting in a spread spectrum signal. Thespectral spreading of the transmitted signal gives rise to the multipleaccess capability of CDMA.

If multiple users transmit spread spectrum signals at the same time, thereceiver will still be able to distinguish a particular user's signal,provided that each user has a unique code and the cross-correlationbetween codes is sufficiently low. Ideally, the cross-correlation shouldbe zero, i.e., the codes should be orthogonal in the code space.Correlating a received signal with a code signal from a particular userwill result in the despreading of the information signal from thatparticular user, while signals from other users will remain spread outover the channel bandwidth.

However, the number of orthogonal codes in a system is limited. As aresult, each cell has a limited number of orthogonal channelizationcodes that are assigned different physical channels. The number oforthogonal channelization codes is dependent upon their spreadingfactor, which is related to the physical channel bitrates. This givesrise to the well-known downlink channelization code limitation inherentin CDMA.

In radio resource management, congestion may occur e.g. on cell level.Several types of Radio Resource Management (RRM) functions exist, suchas handover, power control, admission control and load control. Thefollowing are examples from a radio system using Wideband Code DivisionMultiple Access (WCDMA), but similar things happens also in other mobilesystems and might happen also in other systems.

The purpose of admission control is to ensure that there are free radioresources for an intended call with required signal-to-interferenceratio and bit rate or equivalent. The purpose of load control is tomaintain the use of radio resources of the network within given limits.

Admission control is normally performed when a mobile station initiatescommunications in a new cell, either through a new call or handover.Furthermore, admission control is performed when a new service is addedduring an active call. In general, the admission control procedureensures that there exist a free code to use for a new call and that theinterference created after adding a new call does not exceed aprespecified threshold. Further, the admission control should also checkthat there is enough base station transmission power for the new call.Admission control should be done separately for uplink and downlink.This is especially important if the traffic is highly asymmetric.Typical criteria for admission control are call blocking and calldropping. Call blocking occurs when a new user is denied access to thesystem. Call dropping means that a call of an existing user isterminated.

The basic principle of load control is the same as admission control.While admission control is carried out as a single event, load controlis a continuous process where e.g. the interference is monitored. Loadcontrol measures the load factor of the cell, and, if the predefinedload factor is exceeded, i.e. the cell is congested, then the networkmay e.g. reduce the bit rate of certain users, delay the transmissionfor certain users or drop low priority calls. If there is an underload,load control may increase the bit rates of those users who can handlehigher bit rates.

One version of load control is called channel switching (ChSw) or rateswitching. The main idea is that if a user needs a low bit rate then heshares a common channel with other users. If the user should then needmore capacity he can be switched over to a dedicated channel which iscontinuously reserved just for him. If the user on the other hand shouldneed less capacity he can be switched to a common channel, if the useris using a dedicated channel.

A variant of channel switching is described in WO99/66748. Severalmethods are described on how to determine when to switch. According toone embodiment the buffer fill level can be used; if the queue length inthe buffer is long this is a sign that more capacity is needed and viceversa. Two fixed thresholds in the buffer may be used to indicate whenswitching should take place, in order to create a hysteresis to avoidfrequent switchings.

WO99/66748 further describes the case when there besides the previouslymentioned buffer also exists a packet router buffer in a packet router.In this case it is described a second embodiment with a “back pressure”signal is transmitted from the buffer to the packet router if the queuelength in the buffer becomes too long, whereupon temporarily bufferingtakes place in the packet router buffer rather than in the buffer.

In WO99/66748 these two embodiments can be combined and it can also bechecked if the buffer is full because the connection is temporarilybroken instead of because of increasing traffic. Further, other trafficmeasures can be used, instead or as a complement, e.g. packet arrivaltime, packet arrival rate, packet density, connection's bit rate(s),current number of idle devices or current number of idle spreadingcodes.

Thus, Radio Resource Management adapts the link bit rate after the load,while—given a certain link bit rate—Active Queue Management adapts theload to the link bit rate.

A problem is that the Radio Resource Management and Active QueueManagement may have conflicts in the objectives for the bufferfill-level: Active Queue Management tries to maintain a ‘low’ bufferfill-level to improve interactivity over the link. A small buffer, onthe other hand, makes it difficult for Radio Resource Management to usethe buffer fill-level as a measurement for prediction of future capacityneeds of a link.

SUMMARY OF THE INVENTION

The object with the invention is to design a system with a well behavinginterplay between TCP congestion control, Active Queue Management andRadio Resource Management.

The problem with earlier solutions is that they have not realised thatthis has to be done. They have not understood that problems, such asoscillations, may occur in systems where Active Queue Management andRadio Resource Management work independently. The interplay betweenActive Queue Management and TCP is in prior art fairly well understood.One assumption in prior art is, however, that the capacity of thebottleneck link remains constant. However, this is not in line with thereality of a resource limited system.

In the invention it is noted that the Radio Resource Management and theActive Queue Management may have conflicts in the objectives for thebuffer fill-level: Active Queue Management tries to maintain a ‘low’buffer fill-level to improve interactivity over the link. A smallbuffer, on the other hand, makes it difficult for Radio ResourceManagement to use the buffer fill-level as a measurement for predictionof future capacity needs of a link.

The solution according to the present invention is for upswitch:

-   -   determining link resource status;    -   if link congestion is determined then    -   (a) determining if it is possible to allocate more link        capacity;    -   (b) allocating more link capacity when it is possible to        allocate more link capacity;    -   (c) alleviating link congestion using Active Queue Management        when it is not possible to allocate more link capacity.

An advantage with this method is that it can be ensured that ActiveQueue Management has not asked TCP to reduce its load at the same timeas Radio Resource Management is providing more resources. The risk ofconflicting actions is removed. As a consequence, the allocated capacityis better utilized, because the TCP load is not reduced prior to theup-switch of the capacity.

Further, the queue fill-state may not be a good measurement for RadioResource Management, unless Active Queue Management and Radio ResourceManagement are integrated, as in the proposed method. With the presentmethod, the main measurement for the Radio Resource Management decisionis the up-switch request by Active Queue Management. Other measurements(like user activity statistics) may be used to support the RadioResource Management decision.

The corresponding solution for forced downswitch will then be:

-   -   determining cell resource status;    -   if cell congestion is detected then    -   (a) determining that it is necessary to switch down bit rate or        rates in at least one link;    -   (b) alleviating link congestion using Active Queue Management;        and    -   (c) switching down said bit rate or rates.

An advantage is because Active Queue Management is informed of the ratereduction in advance, it can start to reduce the source rate before thedown-switch, thereby avoiding excessive buffering delays or bufferoverflow.

Further, because the link rate is still high when the Active QueueManagement actions start, the Active Queue Management actions (packetdrop or ECN marking) take effect faster.

DESCRIPTION OF THE DRAWINGS

FIG. 1 discloses a schematic view of a system including the invention

FIG. 2 discloses a method according to the most general aspect of theinvention

DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 illustrates schematically, according to the invention, aUniversal Mobile Telecommunications system (UMTS) network 1 usingWideband Code Division Multiple Access (WCDMA). The UMTS network 1includes a core network 2 and a UMTS Terrestrial Radio Access Network(UTRAN) 3. The UTRAN 3 includes a number of Radio Network Controllers(RNC) 4—of which only one is drawn for the sake of clarity. Each of theRadio Network Controllers 4 is coupled to a set of neighbouring basestations, normally called Node Bs 5. Each Node B 5 is responsible for agiven cell 11 and the controlling Radio Network Controller 4 isresponsible for routing user and signalling data between that Node B 5and the core network 2. A general outline of the UTRAN 3 is given inTechnical Specification TS 25.401 V3.2.0 of the 3rd GenerationPartnership Project. FIG. 1 also illustrates mobile terminals or UserEquipments (UE) 6, a Serving GPRS Support Node (SGSN) 7 and a GPRSGateway Support Node (GGSN) 8. The Serving GPRS Support Node 7 and theGateway GPRS Support Node 8 may e.g. provide packet switched dataservices to the User Equipment 6 via the UTRAN with the Gateway GPRSSupport Node being coupled to e.g. the Internet 9, whereupon the UserEquipment 6 may communicate with a node 10 connected to the Internet 9.

User data received at a Radio Network Controller 4 from the core network2 is stored at a Radio Link Control (RLC) entity 12 in one or morebuffers 13. User data generated at a User Equipment 6 is stored inbuffers 14 of a peer Radio Link Control entity 15 at the User Equipment6. User data (extracted from the buffers) and signalling data is carriedbetween a Radio Network Controller 4 and a User Equipment 6 using RadioBearers. Typically, a User Equipment is allocated one or more RadioBearers each of which is capable of carrying a flow of user orsignalling data. Radio Bearers are mapped onto respective logicalchannels. At a Media Access Control (MAC) layer, a set of logicalchannels is mapped in turn onto a transport channel. Several transportchannels are in turn mapped at the physical layer onto one or morephysical channels—which thus may include one or more links 19—fortransmission over the air interface between a Node B 5 and a UserEquipment 6.

Each link is thus supported by one buffer in the Radio NetworkController 4 and one buffer in the User Equipment 6. Each of the buffers13, 14 is controlled by Active Queue Management (AQM) 16, 17 operatingseparately on each buffer 13, 14 to avoid link congestion. Further, ineach Radio Network Controller 4 is included a Radio Resource Management18, which controls the allocation of radio resources to channels andtries to avoid cell congestion.

According to other embodiments of the invention a buffer may work formore than one incoming and/or outgoing link. This may e.g. be the casein an Internet router. Further, Active Queue Management may work on morethan one buffer simultaneously. In particular, an alternative would beto have a general Active Queue Management working to control the averagetraffic in a whole cell. Finally, of course, Active Queue Managementneeds not be performed on all buffers.

According to the present invention Radio Resource Management and ActiveQueue Management are coordinated. An overview of a process forupswitching is seen in FIG. 2. First, link congestion is detected, block21. Then it is determined if it is possible to allocate more linkcapacity, block 22. If it is possible to allocate more link capacity,then more link capacity is allocated, 23, else link congestion isalleviated using Active Queue Management.

According to one embodiment, link congestion may be detected by settinga congestion threshold Th in the buffer. When the queue length is longerthen the congestion threshold Th, then link congestion is presumed to benear. The natural action would then be, according to prior art, to useActive Queue Management to take action. However, it might happen thatthe congestion is local and that it would be possible to allocate morebandwidth. Thus, according to the present invention, Radio ResourceManagement uses the same congestion threshold as an indication on a needfor higher bit rate and determines if it is possible to allocate morebandwidth. E.g. if the user using the congested link is using a commonchannel that he is sharing with other users, then it might be possibleto instead allocate a dedicated channel just for him. Alternatively, theuser might e.g. be given a higher bit rate within the same common ordedicated channel.

Naturally, other criteria may be used alternatively to a congestionthreshold or in combination therewith to take the decision to switchchannel. Such criteria may be traffic intensity, packet arrival times,time between packets etc.

When Radio Resource Management has determined if it is possible toallocate more bandwidth or not, this should be reported to Active QueueManagement. This can be done by signalling from Radio ResourceManagement to Active Queue Management. Alternatively, a timer can beintroduced on the congestion threshold for the Active Queue Management.Thus, if the congestion threshold has been exceeded for a certain amountof time, then it can be presumed that Radio Resource Management has nofurther bandwidth to allocate and that the Active Queue Management needsto take action.

If the Active Queue Management finds out that more bandwidth isallocated, it takes no action. However, if the Active Queue Managementfinds out that more bandwidth is not allocated, then it may alleviatelink congestion. This may be done by dropping or marking packetsaccording to some predefined algorithm, preferably avoiding to dropsubsequent packets by intent, in order to avoid causing TCP slow startin systems where TCP or similar is used. Marking of packets may be donee.g. by setting an explicit congestion (ECN) flag in the header of apacket. When TCP or similar used and the sender detects that the link iscongested, then TCP will reduce its load and send data packets at alower rate.

The congestion threshold may be fixed, but preferably it is movable. Itcan then be moved according to different primary criteria such as linkcharacteristics i.e.e.g. round trip time (RTT) of the link and data rateor bit rate of the link. The link characteristics may then be used tocalculate link capacity and thereby to set the congestion threshold.This gives a base value Th_(RRM) on the placement of the congestionthreshold. It can be said e.g. that if the bit rate is high, then it canbe permitted to have a longer queue length in the buffer and vice versa,considering that the buffer will be emptied quicker when using a higherbit rate.

In order to employ the Active Queue Management, according to onealternative, secondary criteria may also be used to move the congestionthreshold, in order to give a more detailed placement of the congestionthreshold. Then the congestion threshold Th may be calculated accordingto the following formula:Th=Th _(RRM) ^(+ΔTh) _(AQM)  (1)where ΔTh_(AQM) is an adjustment calculated according to the secondarycriteria according to Active Queue Management. This adjustment may e.g.be calculated by analysing whether a packet has been dropped or not. Ifa packet has been dropped, then ΔTh_(AQM) is increased with a positiveconstant δ, unless the congestion threshold Th has reached a maximumActive Queue Management threshold Th_(AQMmax). If the queue length isdetermined to be less than the congestion threshold by a predeterminedamount—preferably larger than δ in order to cause a hysteresis—thenΔTh_(AQM) is decreased with a positive constant δ unless the congestionthreshold Th has reached a minimum Active Queue Management thresholdTh_(AQMmin). If none of these conditions are met, then ΔTh_(AQM) is leftunchanged.

The maximum Active Queue Management threshold Th_(AQMmax) and theminimum Active Queue Management threshold Th_(AQMmin), may be fixed ormay be adjusted following the base value Th_(RRM) so that:Th _(AQM) =Th _(RRM) +a  (2)Th _(AQM) =Th _(RRM) −b  (3)where a and b are positive constants.

An alternative to analysing whether a packet has been dropped or not ise.g. to look at the buffering delay of each packet. Since the bufferingdelay is independent of bandwidth it may alternatively also be used asthe only means for calculating the congestion threshold.

According to another alternative a maximum Active Queue Managementthreshold Th_(AQMmax) and a minimum Active Queue Management thresholdTh_(AQMmin) are employed in a similar way as above, preferably adjustedfollowing the base value Th_(RRM), but using the base value Th_(RRM) asthe congestion threshold Th:Th=Th _(RRM)  (4)Further, when Active Queue Management is to be employed, then for aqueue fill level above the maximum Active Queue Management thresholdTh_(AQMmax) incoming packets are discarded, for a queue fill level belowthe minimum Active Queue Management threshold Th_(AQMmin) incomingpackets are not discarded, and for a queue fill level between themaximum Active Queue Management threshold Th_(AQMmax) and the minimumActive Queue Management threshold Th_(AQMmin) incoming packets arediscarded or marked with a certain probability.

An alternative to using a probabilistic approach when the queue filllevel lies between the maximum Active Queue Management thresholdTh_(AQMmax) and the minimum Active Queue Management thresholdTh_(AQMmin), is to use a counter to allow only one in every (n+1)thpacket to be dropped.

Other Active Queue Management algorithms may also be used or adapted ina similar way.

Downswitching may be done by Radio Resource Management primarily for tworeasons. A first reason is that less capacity is needed because e.g. auser is needing less bandwidth or goes passive. A second reason isbecause of resource shortage in the cell due to e.g. many new users orhandovers, new services per user, users moving from the cell centre tothe cell periphery (thus requiring a higher power, thus causinginterference to others) etc

In the first case the capacity after the downswitch will normally besufficient. If e.g. a user earlier had been allocated a dedicatedchannel, a hysteresis threshold in the buffer may indicate a low usage.The same threshold as the congestion threshold may of course be used,but it is better to use a hysteresis threshold at a shorter queue lengththan the congestion threshold, to avoid unnecessary frequent channelswitchings. The hysteresis threshold may be fixed, but preferably it ison a fixed distance to the congestion threshold, thus moving when thecongestion threshold is moving.

The user of a dedicated channel may now instead be switched to a commonchannel, which may be sufficient for his needs. Naturally other criteriamay be used alternatively to a hysteresis threshold or in combinationtherewith to take the decision to switch channel. Such criteria may betraffic intensity, packet arrival times, time between packets etc.

In the second case with the forced downswitch, it is a cell congestion.A solution is then to e.g. switch to a lower bit rate for the user in adedicated channel or for all or some of the users in a common channel.Another solution is to switch the user in a dedicated channel into acommon channel—and thus allocating him a lower bitrate. Yet othersolutions are to delay the transmission for certain users, to drop lowpriority calls etc.

Link congestion is, as a consequence, naturally very likely to occurand, depending on the actions taken, probably in more than one linksimultaneously. Thus, in the second case the Radio Resource Managementshould inform the Active Queue Managements for all links or for theaffected links of the intention of a forced downswitch. This ispreferably done by some type of signalling. Said Active QueueManagements can then take appropriate actions to avoid buffer overflow,such as dropping or marking packets.

For the sake of readability, we have in this disclosure explicitlyreferred to specific protocols, systems and functions. It should beclear, however, that the present invention is applicable to a broadrange of systems, protocols and functions with similar properties asdescribed in this invention disclosure:

The present invention is applicable to any wireless system forpacket-data transfer equipped with a resource management function, notonly WCDMA. In fact the system need not even be wireless. However,considering that wireless systems have the greatest problems withallocating resources, wireless systems will have the greatest advantageswith the present invention

Further, the present invention is applicable independently of the choiceof Active Queue Management algorithm. Requirements for the presentinvention are a method for link congestion detection and a packetdropping/marking policy or other way of alleviating link congestion. Anumber of such Active Queue Management algorithms exist.

Further, the present invention is applicable to any type of packet-datatraffic—not only using TCP—which traffic is equipped with an end-to-endload control mechanism. In particular, we note the ongoing efforts tomake non-TCP flows ‘TCP-compliant’ (TCP Friendly Rate Control, TFRC).The invention is also applicable to non-responsive flows, such as UDP.However, the congestion alleviation procedure in the link buffer maythen follow a different pattern, in case the source rate is not reducedas a consequence of packet losses.

1. A method for resource allocation in a packet transmission networkincluding at least one link comprising, the following steps: determininglink resource status; if link congestion is determined then (a)determining if it is possible to allocate more link capacity; (b)allocating more link capacity when it is possible to allocate more linkcapacity; (c) alleviating link congestion using Active Queue Managementwhen it is not possible to allocate more link capacity.
 2. A method forresource allocation according to claim 1, further comprising the stepsof defining in a buffer for said at least one link, a congestionthreshold for packet queue size within said buffer; and using saidcongestion threshold to detect link congestion when the packet queuesize exceeds said congestion threshold.
 3. A method for resourceallocation according to claim 2, further comprising adjusting thecongestion threshold depending on link capacity.
 4. A method forresource allocation according to claim 2 further comprising adjustingthe congestion threshold depending on whether or not a packet isdropped/marked.
 5. A method for resource allocation according to claim2, further comprising adjusting the congestion threshold depending onbuffer delay for a packet in the queue.
 6. A method for resourceallocation according to claim 2, further comprising defining in thebuffer a maximum threshold and a minimum threshold for packet queue sizewithin said buffer.
 7. A method for resource allocation according toclaim 1, further comprising allocating link capacity by changing from acommon channel to a dedicated channel.
 8. A method for resourceallocation according to claim 1, further comprising allocating linkcapacity by changing from a channel with a low bit rate to a channelwith a higher bitrate.
 9. A method for resource allocation according toclaim 1, further comprising determining cell resource status; if cellcongestion is detected then (a) determining that it is necessary toswitch down bit rate or rates in at least one link (b) alleviating linkcongestion using Active Queue Management; (c) switching down said bitrate or rates.
 10. A method for resource allocation according to claim9, further comprising alleviating link congestion for all links.
 11. Amethod for resource allocation according to claim 9, further comprisingalleviating link congestion only for the links where link congestion islikely to occur.
 12. A method according to claim 1, further comprisingif low usage of a link is detected then (a) determining if it ispossible to decrease the link capacity without problems; (b) allocatingless link capacity, when possible.
 13. A method according to claim 1,further comprising alleviating link congestion by dropping or markingpackets.
 14. A method according to claim 2, further comprising usingActive Queue Management separately for each buffer.
 15. A methodaccording to claim 2, further comprising using a general Active QueueManagement for a number of buffers; and controlling the average trafficin the links associated with said buffers.
 16. An arrangement forresource allocation in a packet transmission network including at leastone link the arrangement comprising: a resource management arranged todetermine link resource status and arranged, if a link congestion statusis determined, to determine if it is possible to allocate more linkcapacity, to allocate more link capacity when it is possible to allocatemore link capacity, and to enable alleviation of link congestion usingActive Queue Management when it is not possible to allocate more linkcapacity.
 17. An arrangement for resource allocation according to claim16, wherein the arrangement includes a buffer for said at least onelink, said buffer including a congestion threshold for packet queue sizewithin said buffer, and in that said congestion threshold is arranged todetect link congestion when the packet queue size exceeds saidcongestion threshold.
 18. An arrangement for resource allocationaccording to claim 17, wherein the congestion threshold is arranged tobe adjusted depending on the link capacity.
 19. An arrangement forresource allocation according to claim 17, wherein the congestionthreshold is arranged to be adjusted depending on whether or not apacket is dropped/marked.
 20. An arrangement for resource allocationaccording to any of the claims 17, wherein the congestion threshold isarranged to be adjusted depending on buffer delay for a packet in thequeue.
 21. An arrangement for resource allocation according to any ofthe claims 17, wherein the buffer includes a maximum threshold and aminimum threshold for packet queue size within said buffer.
 22. Anarrangement for resource allocation according to claim 16, wherein theresource management is arranged to determine cell resource status, andarranged, if cell congestion is detected, to determine that it isnecessary to switch down bit rate or rates in at least one link, toenable to alleviate link congestion using Active Queue Management, andto switch down said bit rate or rates.
 23. An arrangement for resourceallocation according to claim 16, wherein the resource management isarranged, if low usage of a link is detected, to determine if it ispossible to decrease the link capacity without problems, and to allocateless link capacity, when possible.
 24. An arrangement for resourceallocation according to claim 17, wherein Active Queue Management isarranged to work separately for each buffer.
 25. An arrangement forresource allocation according to claim 17, wherein Active QueueManagement is arranged to work for a number of buffers and to controlthe average traffic in the links associated with said buffers.